In Chapter 1 it was shown that, for the purposes of color measurement, scenes and other images can be characterized in terms of their color stimuli. In this chapter, the fundamental principles of how such color stimuli can be captured and reproduced by color-imaging systems will be discussed.
Color-imaging systems can be built using an almost unlimited variety of optical, chemical, and electronic components. But regardless of what technologies they incorporate, all imaging systems must perform three basic functions: image capture, signal processing, and image formation (Figure 2.1). These functions are the building blocks of all color-imaging systems, from the simplest to the most complex.
To form a reproduction, an imaging system first must detect light from each original color stimulus and, from that light, produce a detectable image signal. This function, called image capture, can be realized in a number of ways, depending on the technology of the particular imaging system.
For example, an electronic camera, such as a digital still camera, might use a solid-state image sensor, such as a charge-coupled device (CCD), to detect light. Image capture occurs as photons of light are absorbed by the sensor, resulting in the generation of electrons. These electrons are collected into charge packets, and an image signal is produced by a sequential readout of those packets.
In a photographic film, light is captured in the form of a latent image